U.S. patent number 8,229,645 [Application Number 12/326,350] was granted by the patent office on 2012-07-24 for automatic parking system for vehicle.
This patent grant is currently assigned to Hyundai Motor Company. Invention is credited to Jong Ho Lee.
United States Patent |
8,229,645 |
Lee |
July 24, 2012 |
Automatic parking system for vehicle
Abstract
Disclosed herein is an automatic parking system for a vehicle.
The automatic parking system employs a method of generating a
parking trajectory in consideration of the operational performance
of a steering motor connected to the steering wheel of a vehicle,
thus guiding a vehicle through smooth parking and reducing an error
between an ideal parking trajectory and an actual parking
trajectory.
Inventors: |
Lee; Jong Ho (Seongnam-Si,
KR) |
Assignee: |
Hyundai Motor Company (Seoul,
KR)
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Family
ID: |
40754332 |
Appl.
No.: |
12/326,350 |
Filed: |
December 2, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090157260 A1 |
Jun 18, 2009 |
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Foreign Application Priority Data
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Dec 12, 2007 [KR] |
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10-2007-0129290 |
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Current U.S.
Class: |
701/96;
340/937 |
Current CPC
Class: |
B62D
15/0285 (20130101) |
Current International
Class: |
B60T
7/12 (20060101); G08G 1/017 (20060101) |
Field of
Search: |
;701/28,95,96,216,36
;340/426.24,426.25,436,937,938,943,932.2,426.23,933 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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10-2007-0062163 |
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Jun 2007 |
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KR |
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Other References
"Decisional Architectures for Motion Autonomy", Christian Laugier
and Thierry Fraichard, Jul. 10, 2005. cited by examiner .
"Bezier Curves", Paul Bourke, Dec. 1996. cited by examiner.
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Primary Examiner: Trammell; James
Assistant Examiner: Shafi; Muhammad
Attorney, Agent or Firm: Edwards Wildman Palmer LLP Corless;
Peter F.
Claims
What is claimed is:
1. An automatic parking system for a vehicle, comprising: one or
more sensor units configured to detect location information of a
vehicle; a control unit configured to calculate steering angles by
generating a trajectory equation and using the location information
from the sensor unit or units and, generating control command
signals on the basis of the calculation; and a driving unit
comprising a motor unit configured to perform forward rotation or
reverse rotation at one or more predetermined angles in response to
the command signals from the control unit, and a gear unit engaged
with a shaft of the motor unit at a predetermined gear ratio and
configured to generate a predetermined rotation moment; wherein the
control unit generates the trajectory equation based on a plurality
of polynomial curves applied in consideration of performance
limitations of the motor unit.
2. The automatic parking system as set forth in claim 1, wherein
the plurality of polynomial curves is expressed by the following
equation: .function..times..times..times..function..ltoreq..ltoreq.
##EQU00007## where .function..times..times..function. ##EQU00008##
k is an index of a control point for a single polynomial curve, n
is a maximum number of control points, and p.sub.k is the control
point.
3. The automatic parking system as set forth in claim 2, wherein
the plurality of polynomial curves comprises a first polynomial
curve that comprises control points for converting neutral steering
angles into a constant steering angle for a minimum turning radius
and a second polynomial curve that comprises control points for
performing conversion into steering angles for a turning radius of
an arc.
4. The automatic parking system as set forth in claim 1, wherein
control points of a first polynomial curve are symmetrical to
corresponding control points, respectively, of second polynomial
curve adjacent to the first polynomial curve with respect to a
vertical line passing a control point common in the two adjacent
polynomial curves.
5. The automatic parking system as set forth in claim 4, wherein:
the control points constituting the first polynomial curve are
arranged along a rectilinear line at regular intervals in order to
form the neutral steering angles; and the following coordinate
relation equation is applied to the control points constituting the
second polynomial curve in order to form the steering angle for a
turning radius of an arc: .function..times..times..times..times.
##EQU00009##
.function..times..times..times..times..times..times..theta..times..times.-
.times..theta..times..times..times..theta..times..times..times..theta..tim-
es. ##EQU00009.2##
.function..times..times..times..times..times..times..times..times.
##EQU00009.3##
.function..times..times..times..times..times..times..times..times..times.
##EQU00009.4## where R is a turning radius, and .theta..sub.1 is an
angular value that is obtained by equally dividing an angle between
P.sub.3 and P.sub.0 on an arc that has turning radius R and passes
through P.sub.3 and P.sub.0.
6. The automatic parking system as set forth in claim 1, wherein
the sensor units are visual sensors or sonic sensors.
7. A method for automatically parking a vehicle, comprising:
detecting, by one or more sensor units location information of a
vehicle; calculating, by a control unit, steering angles by
generating a trajectory equation and using the location information
from the sensor unit or units and, generating control command
signals on the basis of the calculation; and performing by a motor
in a drive unit forward rotation or reverse rotation at one or more
predetermined angles in response to the command signals from the
control unit, generating, by a gear unit, a predetermined rotation
moment; generating, by the control unit, the trajectory equation
based on a plurality of polynomial curves applied in consideration
of performance limitations of the motor unit.
8. The method as set forth in claim 7, wherein the plurality of
polynomial curves is expressed by the following equation:
.function..times..times..times..function..ltoreq..ltoreq.
##EQU00010## where .function..times..times..function. ##EQU00011##
k is an index of a control point for a single polynomial curve, n
is a maximum number of control points, and p.sub.k is the control
point.
9. The automatic parking system as set forth in claim 8, wherein
the plurality of polynomial curves comprises a first polynomial
curve that comprises control points for converting neutral steering
angles into a constant steering angle for a minimum turning radius
and a second polynomial curve that comprises control points for
performing conversion into steering angles for a turning radius of
an arc.
10. The method as set forth in claim 7, wherein control points of a
first polynomial curve are symmetrical to corresponding control
points, respectively, of second polynomial curve adjacent to the
first polynomial curve with respect to a vertical line passing a
control point common in the two adjacent polynomial curves.
11. The method as set forth in claim 10, wherein: the control
points constituting the first polynomial curve are arranged along a
rectilinear line at regular intervals in order to form the neutral
steering angles; and the following coordinate relation equation is
applied to the control points constituting the second polynomial
curve in order to form the steering angle for a turning radius of
an arc: .function..times..times..times..times. ##EQU00012##
.function..times..times..times..times..times..times..theta..times..times.-
.times..theta..times..times..times..theta..times..times..times..times..the-
ta..times. ##EQU00012.2##
.function..times..times..times..times..times..times..times..times.
##EQU00012.3##
.function..times..times..times..times..times..times..times..times.
##EQU00012.4## where R is a turning radius, and .theta..sub.1 is an
angular value that is obtained by equally dividing an angle between
P.sub.3 and P.sub.0 on an arc that has turning radius R and passes
through P.sub.3 and P.sub.0.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims under 35 U.S.C. .sctn.119(a) priority to
Korean Application No. 10-2007-0129290, filed on Dec. 12, 2007, the
disclosure of which is incorporated herein by reference in its
entirety.
BACKGROUND
1. Technical Field
The present invention relates generally to an automatic parking
system for a vehicle, which is capable of parking a vehicle at an
accurate location.
2. Related Art
An automatic parking system assists a driver in parking his or her
vehicle conveniently and accurately. In general, when parking a
vehicle, a driver considers the locations of one or more obstacles
on the rear part of the vehicle, which can be detected by sensors
(e.g., visual sensors) equipped with the vehicle, and selects an
appropriate parking mode (e.g., parallel parking or perpendicular
parking), and an automatic parking system performs a predetermined
operation accordingly.
FIG. 1 is a diagram showing a parking trajectory of a prior art
automatic parking system.
To parallel park successfully, the vehicle should be parked along a
trajectory having a minimum turning radius. As can be seen from
FIG. 1, the prior art automatic parking system controls a vehicle
so that the vehicle can turn with radius Rc around point C to
parallel park within a narrow space.
The prior art automatic parking system calculates a parking
trajectory using an equation representing the relation between a
circle defining a minimum turning radius on the trajectory and a
rectilinear line tangential to the circle. This parking trajectory
is continuous, but steering angles are applied to respective
turning radii in the form of stepped constant values.
FIG. 2A is a diagram showing an ideal steering angle profile based
on a parking trajectory, and FIG. 2B is a diagram showing an actual
steering angle profile.
In the case of an ideal parking system such as that shown in FIG.
2A, in order to enable parking trajectories in respective stages
(stages a, b, c and d) to form a continuous parking trajectory
during parallel parking, a steering motor for moving a steering
wheel generates a square wave operating signal. However, as shown
in FIG. 2B, there is a problem in that an actual motor-type
steering motor for assisting automatic parking is difficult to
generate square waveforms, unlike an ideal steering motor.
Accordingly, due to the limitations on the performance of the
motor, there are error regions e1, e2 and e3, in which square wave
operating signals are generated. In turn, due to these error
regions, a vehicle cannot be parked along a desired trajectory
accurately.
Here, reference characters shown in the diagrams will be described
in brief, as follows:
a: straight interval without steering angle,
b: initial entry interval using minimum turning radius,
c: rectilinear interval connecting intervals b and d to each other
(tangent line between two circles),
d: final entry interval using minimum turning radius,
TC1, TC2: centers of rotation,
Rc1, Rc2: turning radii for centers of rotation,
e1, e2, e3: quantities of error occurred due to limitations on
motor performance,
P1: ideal parking trajectory which is calculated using the tangent
line of circle-rectilinear line-circle, and
P2: parking trajectory which includes tracking error occurred due
to limitations on motor performance.
FIG. 3 shows graphs comparing displacements of vehicle movements
and vehicle steering angles of the ideal automatic parking system
of FIG. 2A and the actual automatic parking system of FIG. 2B.
Referring to FIG. 3, in the ideal automatic parking system, a
vehicle first starts at point (0 m, 0 m) and finally arrives at
point (-8 m, -3 m) in a rectangular coordinate system. On the other
hand, in the actual automatic parking system, the vehicle first
starts at point (0 m, 0 m) and finally arrives at point (-8 m, -2.5
m). This indicates that the above-described error causes the
vehicle to move 0.5 m in Y-axis less than that of the ideal parking
system.
In order to overcome the problem, a method using empirical inclined
steering angles based on a trial and error scheme instead of the
stepped constant values was proposed. However, this empirical
method has a problem in that it causes significant variations in
error depending on the speed of a vehicle during parallel
parking.
The above information disclosed in this Background section is only
for enhancement of understanding of the background of the invention
and therefore it may contain information that does not form the
prior art that is already known in this country to a person of
ordinary skill in the art.
SUMMARY
Accordingly, the present invention has been made keeping in mind
the above problems occurring in the prior art, and an object of the
present invention is to provide an automatic parking system that is
capable of generating a parking trajectory in consideration of the
operational performance of a steering motor.
In order to accomplish the above object, one aspect of the present
invention provides an automatic parking system for a vehicle,
including one or more sensor units for detecting the location
information of a vehicle; a control unit for calculating steering
angles by generating a trajectory equation and using the location
information from the sensor unit or units and, generating control
command signals on the basis of the calculation; and a driving unit
including a motor unit configured to perform forward rotation or
reverse rotation at a predetermined angle or angles in response to
the command signals from the control unit, and a gear unit engaged
with the shaft of the motor unit at a predetermined gear ratio and
configured to generate predetermined rotation moment; wherein the
control unit generates the trajectory equation with a plurality of
polynomial curves.
The plurality of polynomial curves may be expressed by the
following equation:
.function..times..times..function..ltoreq..ltoreq. ##EQU00001##
where
.function..times..times..function. ##EQU00002## k is an index of a
control point for a single polynomial curve, n is the maximum
number of control points, and p.sub.k is the control point.
Control points of a first polynomial curve are symmetrical to
corresponding control points, respectively, of second polynomial
curve adjacent to the first polynomial curve with respect to a
vertical line passing a control point common in the two adjacent
polynomial curves.
The plurality of polynomial curves may include a first polynomial
curve that comprises control points for converting neutral steering
angles into a constant steering angle for a minimum turning radius
and a second polynomial curve that comprises control points for
performing conversion into steering angles for a turning radius
such as that of an arc.
In order to form the neutral steering angles, the control points
constituting the first polynomial curve are arranged along a
rectilinear line at regular intervals. In order to form the
steering angle for a turning radius such as that of an arc, the
following coordinate relation equation is applied to the control
points constituting the second polynomial curve:
.function..times..times..times..times. ##EQU00003##
.function..times..times..times..times..times..times..theta..times..times.-
.times..theta..times..times..times..theta..times..times..times..times..the-
ta..times. ##EQU00003.2##
.function..times..times..times..times..times..times..times..times.
##EQU00003.3##
.function..times..times..times..times..times..times..times..times.
##EQU00003.4## where R is a turning radius, and .theta..sub.1 is an
angular value that is obtained by equally dividing an angle between
P.sub.3 and P.sub.0 on an arc that has turning radius R and passes
through P.sub.3 and P.sub.0.
The sensor units may be visual sensors or sonic sensors.
It is understood that the term "vehicle" or "vehicular" or other
similar term as used herein is inclusive of motor vehicles in
general such as passenger automobiles including sports utility
vehicles (SUV), buses, trucks, various commercial vehicles,
watercraft including a variety of boats and ships, aircraft, and
the like, and includes hybrid vehicles, electric vehicles, plug-in
hybrid electric vehicles, hydrogen-powered vehicles and other
alternative fuel vehicles (e.g. fuels derived from resources other
than petroleum). As referred to herein, a hybrid vehicle is a
vehicle that has two or more sources of power, for example both
gasoline-powered and electric-powered vehicles.
The above and other features of the invention are discussed
infra.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and other advantages of the
present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
FIG. 1 is a diagram showing a parking trajectory when parallel
parking is performed according to a prior art automatic parking
system;
FIG. 2A is a diagram showing an ideal steering angle profile based
on a parking trajectory;
FIG. 2B is a diagram showing an actual steering angle profile based
on a parking trajectory;
FIG. 3 shows graphs comparing displacements of vehicle movements
and steering angles of the ideal and actual parking systems of
FIGS. 2A and 2B;
FIG. 4 is a diagram showing the construction of an automatic
parking system according to an embodiment of the present
invention;
FIG. 5 is a diagram showing a parking trajectory in consideration
of the characteristics of a steering motor according to an
embodiment of the present invention; and
FIG. 6 shows graphs showing the displacements of vehicle movement
and steering angles according to an embodiment of the present
invention.
DETAILED DESCRIPTION
Reference now should be made to the drawings, in which the same
reference numerals are used throughout the different drawings to
designate the same or similar components.
An embodiment of the present invention will be described with
reference to the accompanying drawings.
FIG. 4 is a diagram showing the construction of an automatic
parking system according to an embodiment of the present
invention.
Referring to FIG. 4, the automatic parking system according to an
embodiment of the present invention includes one or more sensor
units 10, a control unit 20, and a driving unit 30.
The sensor units 10 may be implemented in various ways. For
example, it may be implemented by visual sensors such as cameras
that can detect one or more objects around a vehicle through one or
more captured images. Alternatively, it may be implemented by sonic
sensors such as ultrasonic sensors that can detect one or more
objects around a vehicle through signals reflected from the
objects.
Here, the number and locations of sensor units 10 may vary, and the
sensor units 10 may be freely arranged in conformity with the
characteristics of a vehicle.
The control unit 20 calculates the angle of the steering wheel of a
vehicle and the curvature of an optimum parking trajectory using
object information detected by the sensor units 10, and generates a
control command signal using the resulting value. Furthermore, the
control unit 20 may perform different parking processes according
to parking modes selected by the driver. The following description
will be given, with focus on the parallel parking mode of a
vehicle.
The driving unit 30 performs a predetermined operation in response
to the control command signal from the control unit 10. The driving
unit 30 includes a motor unit 31 configured to perform forward
rotation or reverse rotation at a predetermined angle in response
to the command signal from the control unit 20 and a gear unit 32
engaged with the shaft of the motor unit 31 at a predetermined gear
ratio and configured to generate specific rotation moment.
According to the present embodiment, the control unit 20 creates a
parking trajectory equation using a plurality of polynomial curves
and applies the parking trajectory equation to the automatic
parking system. That is, the method of the present embodiment uses
a control scheme based on a mathematical equation to issue
practical steering angle control commands in consideration of
limitations on the performance of a steering motor, unlike the
prior art method using a tangent line between a circle and a
rectilinear line. The following Equation 1 shows an example of the
polynomial curves according to the present embodiment:
.function..times..times..function..ltoreq..ltoreq. ##EQU00004##
In equation 1,
.function..times..times..function. ##EQU00005## k is the index of a
control point for a single polynomial curve, n is the maximum
number of control points, and p.sub.k is the control point.
Referring to Equation 1, four control points may form one
polynomial curve. The curvature of a trajectory is determined based
on the relative locations of the four control points, and the
steering angle and yaw angle of a vehicle can be calculated using
the curvature of the trajectory.
FIG. 5 is a diagram showing a parking trajectory in consideration
of the characteristics of a steering motor according to an
embodiment of the present invention.
FIG. 5 shows the locations of the control points of two polynomial
curves based on a parking trajectory equation created using the two
polynomial curves.
The trajectory of a vehicle shown in FIG. 5 consists of a first
polynomial curve formed using P.sub.0.about.P.sub.3 and a second
polynomial curve formed using P.sub.3.about.P.sub.6. That is, the
first polynomial curve and the second polynomial curve are separate
polynomial curves.
The control points P.sub.0.about.P.sub.3 are the locations of
control points at which neutral steering angles are converted into
a constant steering angle for a minimum turning radius, and the
control points P.sub.3.about.P.sub.6 are the locations of control
points at which conversion into a steering angle for a minimum
turning radius, such as that of an arc, is performed.
In order to form the neutral steering angle, three control points
P0.about.P2 constituting the first polynomial curve are arranged
along a rectilinear line at regular intervals, as shown in FIG. 5.
Furthermore, in order to form the steering angle for a turning
radius such as that of an arc, a coordinate relation equation, such
as the following Equation 2, may be applied to the control points
constituting the second polynomial curve:
.function..times..times..times..times..times..times..function..times..tim-
es..times..times..times..times..theta..times..times..times..theta..times..-
times..times..theta..times..times..times..times..theta..times..times..time-
s..function..times..times..times..times..times..times..times..times..times-
..times..function..times..times..times..times..times..times..times..times.
##EQU00006##
In Equation 2, R is a turning radius, and .theta..sub.1 is an
angular value that is obtained by equally dividing the angle
between P.sub.3 and P.sub.0 on an arc that has turning radius R and
passes through P.sub.3 and P.sub.0.
In order for the automatic parking system for a vehicle according
to the present embodiment to perform a desired operation, the
continuity in curvature between trajectories should be ensured. In
greater detail, the operation of the motor unit 31 should be
continuous, with the result that steering angles created
accordingly should have continuity characteristics.
In order to achieve continuity between the separate polynomial
curves according to the present embodiment, control points of one
polynomial curve should be symmetrical to corresponding control
points of the adjacent polynomial curve with respect to a vertical
line passing a control point common in the two polynomial curves.
For example, as shown in FIG. 5, P.sub.1 and P.sub.2 should be
symmetrical to P.sub.5 and P.sub.4, respectively, with respect to
the vertical line passing P.sub.3. If the above condition is
satisfied, the polynomial curves can be continuously connected to
each other, and thus steering angles can have continuity.
A graph on the lower portion of FIG. 5 shows variation in steering
angle along the path of movement of a vehicle. That is, the
steering angle of the vehicle gradually increases along the first
polynomial curve, and the steering angle is maintained at a
constant angle along the second polynomial curve. This means that a
circular trajectory is formed with the constant steering angle
generated with the result of the trajectory according to the first
polynomial curve.
As described above, the control unit 20 generates control points
for polynomial curves, calculates steering angles for the control
points, and then controls the movement of a vehicle. Thereafter,
the driving unit 30 performs a steering operation based on the
calculated steering angles.
FIG. 6 shows graphs showing the displacements of movement and
steering angles of a vehicle according to an embodiment of the
present invention.
A target parking location was set to a point (-8 m, -3 m). An
automatic parking system calculated the path of movement of a
vehicle using the trajectory equation. As shown in FIG. 6, the
calculation results show that the parking system moved the vehicle
-3 m along the y axis and -8 m along the x axis (which is indicated
by asterisks on a graph) accurately. Furthermore, the steering
angles were shown not in the form of an ideal square wave signal
but in the form of continuous variation depending on the
characteristics of the motor unit 31.
Although the above-described embodiments of the present invention
have been described, with focus on parallel parking, the technical
spirit of the present invention is not limited thereto. That is,
since the system of the present invention is a system capable of
automatically performing the parking of a vehicle, the same system
is applied to all parking modes (for example, straight forward
parking during perpendicular parking, backward parking during
perpendicular parking, and parallel parking), but is not limited to
a specific mode.
The automatic parking systems according to the present invention
have the advantages of guiding a vehicle through smooth parking and
reducing the error between a predetermined ideal trajectory and an
actual parking trajectory.
Although the preferred embodiments of the present invention have
been disclosed for illustrative purposes, those skilled in the art
will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
* * * * *